Piston pump

ABSTRACT

To provide an efficient piston pump having a small number of parts and simple assembly steps, and consuming less current in achieving a relatively-low ultimate pressure. The piston pump comprises: a suction port ( 28 ) through which gas sucked by varying the volume of a pump chamber ( 22 ) defined by a cylinder ( 12 ) and a piston ( 14 ) fitted in the cylinder ( 12 ) passes as the piston ( 14 ) is reciprocated, an exhaust port ( 20 ) through which the gas discharged by varying the volume of the pump chamber ( 22 ) passes, a suction valve ( 26 ) installed in the suction port ( 28 ) disposed on a piston top, and an exhaust valve ( 18 ) installed in the exhaust port ( 20 ) disposed on a top of the cylinder ( 12 ).

FIELD OF THE INVENTION

This invention relates to a piston pump for compressing gas such as air.More particularly, the present invention relates to a piston pump thatis compact in size and light in weight and is used in an area of arelatively low pressure. The present invention further relates to ablood pressure monitor using this piston pump.

RELATED ART

A blood pressure monitor generally includes a pump capable of sendingcompressed air to fasten an arm, or the like. An automated bloodpressure monitor, in particular, has been widely put on the market inrecent years and a diaphragm type pump has been used (for example,JP-A-63-289276). An example will be explained with reference to FIG. 32.Rotation of a rotary shaft 940 of a motor 942 is converted toreciprocating motion by a crank shaft 938 and is transmitted to aconnecting rod 936 and then to a crasher 954 having a fitting portionadjusted by an iron ball 952. The crasher 954 moves up and down adiaphragm 900. When the diaphragm 900 is pulled down by the crasher 954,air is sucked from external atmosphere through a suction port (a suctionport of a left side chamber is not shown) and further into the diaphragmas a valve 928 opens. When the diaphragm 900 is pushed up by the crasher954, on the other hand, an exhaust valve 918 opens and air is dischargedfrom a discharge port 932.

However, such a diaphragm type pump has a large number of components andneeds complicated assembly processes as well as a large consumed currentat a relatively low ultimate pressure. On the other hand, a piston pumpin the prior art contains mechanical fastening components such as screwsand springs in a similar manner as the diaphragm type pump describedabove, is more expensive, and does not necessarily have high efficiencyat a relatively low ultimate pressure. This invention is made in view ofthe above needs and it is an object to provide a simple and compactpiston pump having high efficiency.

DISCLOSURE OF THE INVENTION

To satisfy such needs, a piston pump according to the present inventionincludes a cylindrical cylinder; a piston reciprocating inside thecylinder; a suction port through which sucked gas passes when a volumeof a pump chamber defined by the cylinder and the piston is changed byreciprocating motion of the piston inserted into the cylinder; anexhaust port through which discharged gas passes when the volume of thepump chamber is changed; a suction valve arranged at the suction portdisposed at a top portion of the piston; and an exhaust valve arrangedat the exhaust port disposed at a top portion of the cylinder.

More concretely, the present invention provides a piston pump, or thelike, having the following features.

(1) A piston pump comprising: a cylindrical cylinder; a pistonreciprocating inside the cylinder; a suction port through which gassucked into a pump chamber defined by the cylinder and the pistonpasses; and an exhaust port through which the gas discharged from thepump chamber passes; wherein the piston pump sucks the gas through thesuction port and discharges the gas through the exhaust port as thevolume of the pump chamber is changed by reciprocating motion of thepiston; wherein the suction port is arranged at a top of the piston witha suction valve, which opens as the volume of the pump chamber isincreased; and wherein the exhaust port is arranged at a top of thecylinder with an exhaust valve, which opens when the volume of the pumpchamber is decreases.

The piston pump according to the present invention includes thecylindrical cylinder, the piston reciprocating inside the cylinder, thesuction port through which gas sucked into the pump chamber defined bythe cylinder and the piston passes, and the exhaust port through whichgas discharged from the pump chamber passes. The cylindrical cylindermay be in a so-called tubular shape such that an outside the cylinderhas a shape of a circular cylinder and an inside thereof is hollow. Theoutside may have an entirely different shape. The piston is insertedinto this cylinder. The piston preferably has an outside shape profilingthe inside shape of the cylinder. The piston may reciprocate in an axialdirection of the cylinder along the inner wall of the cylinder and thepiston more preferably has a shape so that this reciprocating motion canbe smoothly carried out.

A pump chamber encompassed by the piston (especially, a top portion (orhead)), the cylinder inner wall and the cylinder top portion (or distalend portion) is defined inside the cylinder. Therefore, the volume ofthe pump chamber varies depending on the position of the piston in theaxial direction on the cylinder side.

The gas to be sucked and discharged may be ordinary gas such as air,oxygen, nitrogen, and carbon dioxide, or may be that which is subject tophase changes depending on conditions such as vapor and freon, or amixture thereof, or that mixed with solid substance such as a particle.Furthermore, not only the gas but also fluid such as liquid can beapplied to the piston pump according to the present invention. Suctionand discharge to and from the pump chamber is mainly conducted inassociation with the change of the volume of the pump chamber, and thesuction port and the exhaust port through which the gas sucked anddischarged passes are arranged in at least one element forming the pumpchamber (hereinafter called “forming element”). These ports (hereinaftercalled “openings”) may be single or plural, or one opening may operateas the suction port and the exhaust port. A plurality of openings mayoperate as the suction port and the exhaust port. These openings mayopen to the pump chamber side at least for a predetermined time or at acertain timing in each forming element in which the opening is formed.

To change the volume of the pump chamber by the reciprocating motion, tosuck the gas from the suction port and to discharge the gas from theexhaust port, the piston can reciprocate while keeping predeterminedair-tightness with the cylinder inner wall on which it slides. Thepredetermined air-tightness is air-tightness sufficient enough for thepiston pump. The reciprocating motion of the piston is conducted by thedriving force mainly transmitted from outside to the piston. Thepressure of the pump chamber drops in comparison with the externalpressure when the piston moves by the external driving force whilekeeping air-tightness and the volume of the pump chamber increases.Therefore, the suction valve provided to the suction port may open. Thesuction valve can be arranged at the top portion (or head) and/or anintermediate part or a bottom part of the piston but is preferablyarranged at the top portion. For, the minimum volume of the pump chambercan be much more reduced. When the volume of the pump chamber isdecreased due to the motion of the piston in the opposite direction, theexhaust valve provided to the exhaust port may open. This exhaust valvemay be arranged at the top portion (or distal end or head) of thecylinder.

In this way, when the suction port having the suction valve is arrangedat the top of the piston and the exhaust port having the exhaust valveis arranged at the top of the cylinder, arrangement efficiency can beimproved in comparison with the case where both suction port and exhaustport are arranged at the top of the piston (or at the top of thecylinder) and the diameters of the cylinder and the piston can bedecreased.

The flow of the gas is likely to become unidirectional and a smooth flowcan be expected. When the cylinder top portion is flat and the topportion of the piston is flat, too, for example, mutual interferencedoes not easily occur when the piston exists at the upper dead point andthe minimum pump chamber volume can be kept small. Eventually, thecompression ratio can be increased even at the same stroke. The suctionport and the exhaust port described above may be mere holes (or ports)inclusive of circular openings formed in a flat plate. They may beformed by a section of a hose, a tube, a pipe, and so forth. Though thesuction valve and the exhaust valve are not limited, a flap valve or thelike is suitably used and other valves of arbitrary types can be used,too. For example, a part of the periphery of a flat, flexible sheet-likevalve is fixed in a hinge form and opening/closing of the valve may beconducted. It is also possible to use a valve having an umbrella shapeand opened/closed due to flexibility of the umbrella surface.

(2) The piston pump according to (1), wherein the suction valve isarranged on a side of the pump chamber.

The arrangement in which the suction valve is arranged on the pumpchamber side may represent a valve that is arranged on the pump chamberside of the piston, whose suction port is closed when the suction valvecomes into close contact with the piston and is opened when force thatseparates the suction valve from the piston acts. For example, it is thecase where the suction valve is arranged at the top portion of thepiston and is arranged on the pump chamber side of the wall forming thetop portion. More specifically, when a flap type valve is arranged onthe pump chamber side of the wall forming the top portion of the pistonand is so disposed as to cover the suction port formed in the wallforming the top portion, the suction valve can be opened without using ahigh control technology, in particular, when the pump chamber is at alower pressure than the external pressure and can be closed when thepump chamber is at a higher pressure than the external pressure. Here,the external pressure may mean the pressure or the space on the oppositeside to the pump chamber side of the suction port or the atmosphericpressure or may mean the pressure or the space on the feeding side ofthe gas to be sucked.

(3) The piston pump according to (1) or (2), wherein the exhaust valveis arranged on an opposite side to the pump chamber of the top of thecylinder.

The arrangement in which the exhaust valve is arranged at the topportion of the cylinder on the opposite side to the pump chamber maymean that the exhaust valve is arranged at the top portion of thecylinder and is arranged on the wall forming the top portion on theopposite side to the pump chamber. Here, the top portion of the cylinderis preferably a portion that forms one of the ends of the cylinder inthe axial direction. The axial direction is more preferably a directionextending along the direction of the reciprocating motion of the piston.The top portion of the cylinder is preferably a member that closes oneof the ends of the cylinder and is more preferably a member that forms aplate or a wall.

When the flap type valve is arranged on the opposite side of the wallforming the top portion of the cylinder to the pump chamber side and thevalve is so installed as to cover the exhaust port, the exhaust valvecan be closed without using a particularly high control technology whenthe pressure of the pump chamber becomes lower than external air. Whenthe pump chamber reaches a higher pressure than external air, theexhaust valve can be opened. Here, the external air may mean the spaceor the pressure of the exhaust port on the opposite side to the pumpchamber side and may mean the space or the pressure on the feed side ofthe gas to be exhausted. As described above, because the suction valveand the exhaust valve operate in the interlocking arrangement, the pumpcan be efficiently operated.

(4) The piston pump according to any one from (1) to (3), wherein thepiston has an opening communicating with the suction port on an oppositeside to the pump chamber, wherein the opening is arranged so as to allowair sucked through the suction port into the pump chamber to pass and aplenum capable of storing the air to communicate with the opening; andwherein the plenum is encompassed by an enclosure having at least oneplenum suction port.

Here, the plenum may include a space such as the air chamber. Theopening portion communicating with the suction port may be open to theplenum so as to be allowed to suck air from the plenum. This plenum isencompassed by an enclosure being composed of one or a plurality ofwalls, and such an enclosure may define the principal portions of theplenum. The shape of the enclosure may include a rectangle, a circle ortheir combination and a so-called boxed shape can encompass the plenum.The plenum suction port may be an opening formed in the plenum. Forexample, the plenum suction port may include an opening portion formedin the enclosure of the plenum. A valve that can be opened and closedmay be disposed in this opening portion.

(5) A piston pump including a cylindrical cylinder having a top portion;a piston reciprocating inside the cylinder; a suction port through whichgas sucked into a pump chamber defined on a side of the top portion ofthe cylinder by the cylinder and the piston passes; and an exhaust portthrough which the gas discharged from the pump chamber passes; whereinthe piston pump sucks the gas from the suction port and discharges thegas through the exhaust port as a volume of the pump chamber is changedby reciprocating motion of the piston; wherein the suction port isarranged at the top portion of the cylinder with a suction valve, whichopens when the volume of the pump chamber is increased; and the exhaustport is arranged at the piston with an exhaust valve, which opens whenthe volume of the pump chamber is decreased.

(6) The piston pump according to (5), wherein the suction valve isarranged on a side of the pump chamber.

(7) The piston pump according to any one from (1) to (6), wherein thepiston engages with a coupling member in such a manner that the couplingmember is capable of turning in a circumferential direction thereof, andwherein the coupling member is connected to a connecting member drivensuch that the engaged piston is reciprocated inside the cylinder.

The piston may be connected to the connecting member through thering-like coupling member capable of rotating in the circumferentialdirection of the piston. Being capable of turning in the circumferentialdirection of piston may represent the state where the coupling member iscapable of turning clockwise and/or counterclockwise. The turning may beturning of one round or partial turning. The coupling member may be amember that connects the piston and the connecting member and transmitsmechanical force from the connecting member to the piston while keepinga predetermined degree of freedom with the piston. The coupling membermay include a coupling member (inclusive of a coupling ring oflater-appearing embodiments) disposed on the side other than the topportion (that is, end portion of piston positioned on pump chamberside), for example, the base bottom side (that is, the sidecorresponding to far side from pump chamber), and capable of rotating inthe circumferential direction of the piston (for example, incircumferential direction when piston is a circular cylinder piston).The connecting member (which may include a connecting ring inlater-appearing embodiments) connected to this coupling member may bedriven by external driving force. This external driving force mayinclude any kind and is not limited. For example, it may be drivingforce by a crank shaft connected to a motor shaft. The crank shaftconverts the rotary motion to the reciprocating motion.

(8) The piston pump according to (7), wherein the piston comprisestherein a recess portion formed continuously in the circumferentialdirection of the piston and engaged with the coupling member, the recessportion including at least a part of a first predetermined sphericalsurface; wherein the coupling member has a projection portion formedcontinuously in the circumferential direction such that the projectionportion corresponds to the recess portion, the projection portionincluding at least a part of a predetermined second spherical surface toengage with the recess such that the projection portion is capable ofturning in the circumferential direction and in an axial direction; andwherein the piston reciprocates when the projection portion and therecess portion engage with each other so as to transmit driving forcefrom the connecting member to the piston.

The inside of piston may include the side that does not face the innerwall of the cylinder. In a piston having a circular cup-like shape oneof the ends of which is closed, for example, the term may include theinside of the cup or the cylindrical hollow portion. The inside recessportion may contain a groove that is recessed to a portion correspondingto the inner wall of the cup. The recess of this recess portion morepreferably has substantially the same radius of curvature as that of aspherical surface formed when a ball is inscribed with the inside of thecup. The projection portion of the coupling member more preferably hassubstantially the same radius of curvature as that of a sphericalsurface that is substantially the same, or a little smaller, so that therecess portion can be engaged. The recess portion and/or the projectionportion are more preferably continuous in the circumferential directionof the piston.

(9) The piston pump according to any one from (1) to (8), wherein atleast a portion of the piston sliding on an inner wall of the cylinderis composed of a self-lubricating material.

The construction in which at least a portion of the piston sliding onthe inner wall of the cylinder is formed of a self-lubricating materialmay be a construction in which a member formed of such aself-lubricating material is disposed on the inner wall side of thecylinder, that is, around the outer periphery of the piston. Theconstruction may include a construction in which the self-lubricatingmaterial is coated around the outer periphery of the piston. Theself-lubricating material need not always be disposed around the entireouter periphery but may be disposed partially. To make the lubricatingperformance uniform in the peripheral direction, the material ispreferably arranged in the entire outer periphery and may be arranged ina single or a plurality of layers such as a belt wound on the piston,whenever necessary. The self-lubricating material has by itself theself-lubricating property and may be a mixture of the self-lubricatingmaterial with a lubricant in other cases, and they can be usedappropriately without limitation. It is possible, for example, to use acomposite material of an organic solid lubricant such as Teflon(registered trade mark) and an inorganic solid lubricant such asmolybdenum disulfide and graphite. Furthermore, a lubricant impregnatedwith a liquid such as oil or silicon may be suitably used. Polymermaterials and synthetic resins explained in later-appearing embodimentsmay also be included. These materials can be used for the piston, thecylinder, the piston head, the cylinder head, the coupling member, theconnecting member, the crank shaft, the housing and other components.

The materials excellent in the sliding performance can be used not onlyfor the piston but also for other members (for example, the cylinder,the coupling member, the connecting member, etc) and their counter-partmembers. It is preferred to use the material described above for both ofthem depending on the sliding condition. Not only the material but alsothe surface characteristics (surface coarseness, for example) of thematerial are sometimes important.

(10) The piston pump according to any one from (1) to (9), wherein thecylinder comprises a top plenum defined by a top enclosure fixed to thetop portion of the cylinder and a motor housing fixed at a positionspaced apart by a predetermined distance from the top portion such thatthe cylinder is connected and fixed to at least a part of the motorhousing; wherein the motor housing is composed of a base portion fixedto the cylinder such that the base portion holds a motor for driving thepiston so as to reciprocate inside the cylinder and a cover portiondisposed along the base portion such that the cover portion fastens themotor by sandwiching the motor with the base portion; and wherein thecover portion and the base portion are engaged with a connectingmechanism capable of engagement and disengagement.

The top enclosure may include closure members (which may includecylinder head or head plate, for example) of the top portion of thecylinder and walls encompassing the top plenum. For example, the topenclosure may include the enclosure member described above as a basematerial, side walls having a predetermined height and extendingsubstantially vertically on and over the base material and a ceilingplate expanding substantially parallel to the base material on the sidewalls. The top plenum may include a space such as an air chamber. Thetop enclosure may include an exhaust or discharge port opening to theoutside of a piston pump system and communicating with the plenum. Thisdischarge port may take a tubular shape as a discharge port. A portionspaced apart by a predetermined distance from the top portion of thecylinder may exist at a position a little spaced apart from the topportion along the cylinder. In other words, the motor housing is morepreferably fixed to the cylinder but not directly to the cylinder topportion. When the cylinder is used as a structure, the weight or size ofthe overall piston pump can be reduced. Therefore, the motor housing isfixed to the cylinder and the motor fixed to this motor housing is fixedto the cylinder.

(11) The piston pump according to any one from (1) to (10), wherein thepiston pump is connected to a blood pressure monitor.

(12) A piston pump in which a piston reciprocates inside a cylinderhaving a cylinder head for pressurization, the piston pump ischaracterized in that:

-   -   <1> an inner diameter of the cylinder is not exceeding        approximately 20 mm;    -   <2> a throughput of the piston pump is not exceeding        approximately 6.0 liters/min;    -   <3> pressurization characteristics thereof can be maintained        even after approximately 10,000 reciprocating motions of the        piston; and    -   <4> the cylinder and the cylinder head are non-mechanically        coupled.

The construction in which <1> the inner diameter of the cylinder isequal to or not greater than approximately 20 mm in the piston pump thatreciprocates inside the cylinder having the cylinder head and conductspressurization may be a construction in which the inner diameter of thecylinder used as a main component of the piston pump is equal to or notgreater than approximately 20 mm. More preferably, the cylinder innerdiameter of a pump for a wrist blood pressure monitor is equal to or notgreater than approximately 8.5 mm and the cylinder inner diameter of anupper arm blood pressure monitor is equal to or not greater thanapproximately 18 mm. Here, the cylinder head may represent a member(inclusive of component) at the cylinder top portion and may include amember (inclusive of component) directly bonded to the member of thecylinder top portion. The size of the piston pump according to thepresent invention can be made compact due to its structure and itscomponent structure. The construction in which <2> the dischargethroughput of the piston pump is equal to or not greater thanapproximately 6.0 liters/min may represent that the discharge throughputwhen the pump is operated under a non-loaded condition is equal to ornot greater than approximately 6.0 liters/min. More preferably, thedischarge throughput of the piston pump is equal to or not greater thanapproximately 1.0 liter/min in the case of a wrist type pump and isequal to or not greater than approximately 5.5 liters in an upper armtype pump. The construction in which <3> pressurization characteristicscan be maintained even by reciprocating motion of the piston ofapproximately 10,000 times may represent that predetermined performanceof the piston pump such as a maximum ultimate pressure and/or a pressureultimate speed can be maintained even when the piston is reciprocatedapproximately 10,000 times. More preferably, the pressurizationcharacteristics can be maintained even by the reciprocating motion ofthe piston of at least approximately 30,000 times. The construction inwhich <4> the cylinder and the cylinder head are non-mechanicallycoupled may represent that the cylinder head formed by bonding the valveplate and the manifold constituting the cylinder and the end face of thetop portion of the cylinder are coupled by a non-mechanical method suchas bonding, welding, deposition, and the like. Bonding is particularlypreferably made by welding and/or deposition. The cylinder and thecylinder head may well be bonded by welding and/or deposition withoutusing screws or fitting using springs. According to such a construction,seal performance can be easily secured and the pump can be renderedcompact. For, when mechanical bonding members such as the screws areused, it is necessary in some cases not only to bore screw holes or tosecure spaces for screw threads but also to use screws capable ofsecuring air-tightness.

(13) A method of producing a piston pump including a cylindricalcylinder, a piston reciprocating inside the cylinder; a suction portthrough which gas sucked into a pump chamber defined by the cylinder andthe piston passes and an exhaust port through which the gas dischargedfrom the pump chamber passes; the method comprising the steps of:producing a piston pump pre-assembly comprising the cylinder and acylinder top portion in which the exhaust port is formed; conducting aleakage inspection of the piston pump pre-assembly; and producing apiston pump by further assembling components to the piston pumppre-assembly.

The piston pump pre-assembly may include the cylinder and the cylindertop portion in which the exhaust port is formed, and may be asemi-finished product of the piston pump containing those componentswhich are necessary for conducting a leakage inspection of the pistonpump. The step of forming this piston pump pre-assembly does not requireassembly using screws and springs. In other words, the production of thepiston pump pre-assembly may be carried out by conducting combinationinclusive of butting of components and assembling and conductingnon-mechanical bonding such as bonding, welding, deposition, and soforth. The leakage inspection of the piston pump pre-assembly isnecessary for the piston pump but need not always be made for thefinished product of the piston pump. The production of the piston pumpby further assembling components to the piston pump pre-assembly maymean that those components which are once removed from the piston pumppre-assembly in the subsequent step of finishing the piston pump neednot be assembled again.

The piston pump to be connected to the blood pressure monitor mayrepresent a piston pump that is exclusively used for an instrument formeasuring the blood pressure. However, the piston pump does not excludeother applications and may include the application of the measurement ofthe blood pressure. The piston pump used for the instrument formeasuring the blood pressure may include a pump for generating an airpressure necessary for pressing (fastening) the portion necessary forthe blood pressure measurement such as the wrist or the arm of people.

(14) A blood pressure monitor utilizing the piston pump according to anyone from (1) to (12).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing in section a piston pump according to anembodiment of the present invention under the state where a motorhousing is open.

FIG. 2 is a view showing the piston pump according to the embodiment ofthe present invention under the state where a side surface of the pistonpump is partially shown in section by removing a part of components.

FIG. 3 is an expanded view of the piston pump according to theembodiment of the present invention when the piston pump is expandedinto components.

FIG. 4 is a sectional view of a piston as a component of the piston pumpaccording to an embodiment of the present invention.

FIG. 5 is a perspective view when the piston as a component of thepiston pump according to the present invention is viewed from its top.

FIG. 6 is a perspective view when the piston as a component of thepiston pump according to the present invention is viewed from its basebottom side.

FIG. 7 is a side view of a connecting ring as a component of the pistonpump according to the embodiment of the present invention.

FIG. 8 is a sectional view of the connecting ring as a component of thepiston pump according to the embodiment of the present invention.

FIG. 9 is an upper surface view of the connecting ring as a component ofthe piston pump according to the embodiment of the present invention.

FIG. 10 is a perspective view of the connecting ring as a component ofthe piston pump according to the embodiment of the present invention.

FIG. 11 is a front view of the connecting ring as a component of thepiston pump according to the embodiment of the present invention.

FIG. 12 is a schematic sectional view for explaining the function of theconnecting ring as a component of the piston pump according to theembodiment of the present invention.

FIG. 13 is an X-X′ sectional view of FIG. 12.

FIG. 14 is a sectional view showing deformation of a recess portion ofthe piston when the connecting ring shown in FIG. 13 is taken out.

FIG. 15 is a schematic view when deformation of the recess portion ofthe piston shown in FIG. 14 is viewed from the base bottom side of thepiston.

FIG. 16 shows a gas leakage inspection apparatus of the piston pump, anda method for the apparatus, according to the embodiment of the presentinvention.

FIG. 17 is a view showing in a section a piston pump pre-assembly usedfor the gas leakage inspection of the piston pump according to thepresent invention.

FIG. 18 is a graph showing the relation between an ultimate pressurereached by the piston pump according to the embodiment of the presentinvention and a consumed current.

FIG. 19 is a flowchart showing a production method of the piston pumpaccording to the present invention inclusive of a gas leakage inspectionstep.

FIG. 20 shows a section of the piston pump according to the embodimentof the present invention under the state where a cover portion of themotor housing is closed.

FIG. 21 shows a section of the piston pump according to the embodimentof the present invention under the state where suction/exhaust isreversed and a cover with pin of the motor housing is opened.

FIG. 22 is a perspective view showing a production form of a motorhousing having a cover with pin and used for the piston pump accordingto the embodiment of the present invention.

FIG. 23 is a perspective view showing an assembly form of the motorhousing having a cover with pin and used for the piston pump accordingto the embodiment of the present invention.

FIG. 24 is a perspective view showing the assembly form when a motorengaging with a piston is inserted into a motor housing having a coverwith pin and used for the piston pump according to the embodiment of thepresent invention.

FIG. 25 is a perspective view showing an overall form of the motor shownin FIG. 24.

FIG. 26 is a perspective view under the state where the piston pumpaccording to the embodiment of the present invention has been assembled.

FIG. 27 is an upper surface view showing a control principal portion ofa blood pressure monitor to which the piston pump according to theembodiment of the present invention can be fitted.

FIG. 28 is a sectional view of a substrate of the control principalportion shown in FIG. 27.

FIG. 29 is an upper surface view of a pressurization portion when adiaphragm pump according to the prior art is fitted to the controlprincipal portion shown in FIG. 27.

FIG. 30 is an upper surface view of the control principal portion whenthe piston pump according to the present invention is fitted to thecontrol principal portion shown in FIG. 27.

FIG. 31 shows a section of the piston pump according to the embodimentof the present invention under the state where a crank chamber at acylinder lower part is sealed and a motor housing equipped with a crankchamber suction port is closed.

FIG. 32 is a view showing, partly in section, a diaphragm pump of aComparative Example.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will be hereinafter explained in further detailabout an embodiment thereof with reference to the drawings. Theembodiment represents concrete component names, materials, numericalvalues, etc, as a preferred example of the present invention but thepresent invention is not limited to the embodiment.

FIG. 1 is a sectional view of a piston pump 10 according to anembodiment of the present invention. The piston pump 10 of thisembodiment mainly comprises a housing for accommodating a motor 42,constituted by a housing substrate material 44 and a cover 47, a piston14 driven by the motor 42, a cylinder 12 into which the piston 14 isinserted and a valve plate 16 forming a cylinder top portion, and amanifold 30 deposited to the valve plate 16. The motor 42 positioned ata lower left position in the drawing is supported by the cover 47 insuch a manner as to strike the lower part of the housing substratematerial 44. A degree of freedom of the motor 42 in a transversedirection in the drawing is restricted by an upward protuberance 49formed at a substantial center of the cover 47 and the degree of itsfreedom in a rotating direction is restricted as the motor 42 issandwiched between the housing substrate material 44 and the cover 47.The cover 47 is connected by a side member 45 playing the role of ahinge in such a manner as to hang down from the housing substratematerial 44. The cover 47 closes the housing by sandwiching the motor 42with the housing substrate material 44 as described above and fixes themotor 42 inside the housing. At this time, a protuberance 43 on theright side of a protuberance portion extending upward at the extremeright of the cover in the drawing engages with an opening 51 formed at alower part of a side member 46 existing at a position opposing the sidemember 45 to prevent the cover 47 from falling down in the drawing andto keep it under the closed state. The cylinder 12 is positioned on theright side in the drawing, is coupled and fixed with the housing(particularly, the housing substrate material 44) and extends verticallyin the drawing. The piston 14 is inserted into the cylinder 12 andreciprocates in an axial direction that is the vertical direction in thedrawing. The valve plate 16 is coupled with and arranged on the cylinder12 in the drawing by depositing a deposition portion 15 so as to keepgas-tightness and forms the top portion of the cylinder 12. The valveplate 16 has the manifold 30 that is deposited to a deposition portion17 at the upper part in the drawing. A space 31 defined by the manifold30 and the valve plate 16 is a chamber for air exhausted and thedeposition portion 17 is deposited in such a manner as to keepair-tightness of this chamber. In other words, the space 31 functioningas a top plenum is defined by the valve plate 16 and the manifold 30that together function as a top enclosure. An air outlet (discharge port32) of the chamber constituted by the space 31 is disposed on the leftside of the manifold 30 in the drawing.

The rotation of the driving shaft 40, that extends to the right in thedrawing, of the motor 42 accommodated in the housing is transmitted tothe crank shaft 38 pressure-fitted into the driving shaft 40. Becausethe driving shaft 40 is press-fitted to the position deviated by apredetermined distance L from the center of the crank shaft 38 having acylindrical shape, however, the rotary motion is converted to thereciprocating motion in the vertical direction (see FIG. 2). The crankshaft 38 is so fitted into the ring opening portion 36 c (see FIG. 8) ofthe connecting ring 36 as to be capable of rotating. The outer peripheryof the crank shaft 38 slides with the inner surface of the open portionof the connecting ring 36 when the crank shaft 38 rotates. For, theconnecting ring 36 is fixed in the rotating direction described aboveand cannot follow and rotate. The driving shaft 40 is eccentricallyconnected to the crank shaft 38, the axial position of the driving shaft40 is fixed by a bearing of the motor 42 and the motor 42 is fixed tothe housing. Therefore, the connecting ring 36 changes its positionrelative to the housing, that is, relative to the fixed cylinder 12 butis restricted by the coupling ring 34 formed integrally with theconnecting ring 36, the piston 14 to which the coupling ring 36 isconnected and the inner wall of the cylinder 12 into which the piston 14is fitted, thereby causing the reciprocating motion of the piston. Thecoupling ring 34 integrally bonded with the connecting ring 36 absorbsto a certain extent the motion of the connecting ring 36 due to thecrank shaft 38 in the foreground and depth sides of the drawing byfreedom of the coupling ring 34 in the piston circumferential directionand by the spherical outer peripheral surface of the coupling ringreceived by a spherical seat 37 of the piston inner surface in thecircumferential direction and transmits this motion to the piston 14 asthe vertical reciprocating motion in the drawing (see FIG. 4). In otherwords, the rotation of the motor 42 allows the piston 14 fitted into thecylinder 12 to reciprocate in the vertical direction in the drawing.

When the piston 14 is pulled down in the drawing, the volume of the pumpchamber 22 defined by the top portion of the piston 14, the inner wallof the cylinder 12 and the valve plate 16 at the top of the cylinderincreases and the pressure inside the pump chamber 22 drops.Consequently, an umbrella-shaped suction valve 26 inserted into a hole29 formed at the center axis position of the piston 26 opens and air isintroduced through the suction port 28 from the external atmospherebelow the piston 14. The coupling ring 34 has a ring-like shape and itscenter portion is hollow with the exception of the connection portionwith the connecting ring 36. Therefore, air sucked from the suction port28 comes from the hollow portion 35 of the piston 14 (see FIG. 4). Thisair passes through the spaces on both of the sides (or one of the sides)of the connection portion of the coupling ring 34 pressure fitted intothe piston 14 and from the lower side (or the base bottom side) of thepiston 14. The crank shaft 38, etc, is arranged and accommodated in thehousing (housing substrate material 44, side members 45 and 46 and cover47) below the piston 14 but has sufficient opening because a partitionplate 48 has openings. Consequently, air can be sucked substantiallyfreely from below the piston pump 10. Incidentally, FIG. 1 shows thestate where the piston 14 is pulled down almost to the lower dead point.

The volume of the pump chamber 22 decreases while the pressure insidethe pump chamber 22 increases when the piston 14 is pulled up in thedrawing. Therefore, air having a high pressure inside the pump chamberopens the umbrella-shaped exhaust valve 18 fitted into the hole 24disposed at a position of the valve plate 16 corresponding to thecylinder center axis and arranged at the top (or distal end portion) ofthe cylinder 12 through the exhaust port 20 opened by the valve plate 16arranged at the top (or distal end portion) of the cylinder 12. Airinside the pump chamber is from thence exhausted. Air so exhausted isdischarged from the discharge port 32 through the space 31 inside themanifold.

In the embodiment, the portions that frequently slide are a set of thecrank shaft 38 and the connecting ring 36 and a set of the piston 14 andthe cylinder 12. To satisfy their sliding characteristics, an organicmaterial such as a synthetic resin is preferably used and its surfacecoarseness is as small as possible and is preferably a mirror surface orapproximate to the mirror surface. More concretely, the crank shaft 38,the connecting ring 36 and the piston 14 of this embodiment use “Lubmer”(registered trade mark) of Mitsui Petrochemical Co., Ltd. This Lubmer isa specific polyolefin resin having high sliding characteristics. It isalso possible to use ultra-high molecular weight polyethylene (forexample, “Hizex Million”, a product of Mitsui Petrochemical Co., Ltd),polyacetal and nylon (6, 66) as the sliding member besides the specificpolyolefin resin described above. In this embodiment, the cylinder 12,the valve plate 16 and the manifold 30 that are integral with thehousing are formed of a polymer material comprising “Stylac” (registeredtrade mark) of Asahi Kasei K. K. These components are made of the sameABS in view of their fusibility. The valve uses an ordinary NBR rubber.

Each bonding member shown in the drawing is bonded by ultrasonicdeposition at a respective deposition portion.

FIG. 2 is a partial sectional view of the piston pump of the embodimentwhen a part of the components viewed from the right side of FIG. 1 isremoved. The uppermost rectangular component is the manifold 30. Themanifold 30 and the valve plate 16 below the former are bonded to eachother by ultrasonic deposition capable of keeping air-tightness in thesame way as bonding between the cylinder 12 integrated with the housingbelow the valve plate 16 and the valve plate 16. The piston 14 insertedinto the cylinder 12 has the suction port 28 and the suction valve 26(see FIG. 1). The spherical seat 37 exists in the recess portion formedin the inner peripheral surface of the piston 14 below the piston 14(see FIG. 4). The spherical seat 37 is finished into the annularspherical shape so that it mates with the convex outer circumference ofthe coupling ring 34 that is brought into contact with the sphericalseat 37. The coupling ring 34 is press-fitted into this recess. Theconvex of the coupling ring 34 and the upper and lower tilt portions ofthe recess in which the coupling ring 34 exists and the coupling ring 34move up and down the piston 14 without falling off from this recess. Theposition of the driving shaft of the motor 42 does not change withrespect to the housing in the drawing. Therefore, the connecting ring 36moves up and down and to the right and left in the drawing with respectto the housing when the motor 42 rotates. When moving up and down, theconnecting ring 36 simultaneously moves up and down the piston 14. Whenthe connecting ring 36 moves to the right and left, however, theconnecting ring 36 undergoes deformation at the joint portion with thecoupling ring 34 because the cylinder 12 restricts the movement of theconnecting ring 36. It is therefore possible to absorb this motion, orto absorb this motion with the coupling ring 34 due to the slip in thespherical seat 7. Because the coupling ring 34 has freedom to a certainextent in its circumferential direction, it can absorb the movement ofthe driving shaft 40 of the motor 42. Therefore, the piston pump canflexibly cope with unexpected movement and deformation of the piston 14and the crank shaft 38 because freedom for absorbing the movement issecured in various directions.

FIG. 3 is a view when the piston pump 10 of the embodiment is expandedinto each component. The piston pump 10 serially includes, from above,the manifold 30 having the discharge port 32, the valve 18 as theexhaust valve inserted into the hole 24 of the valve plate 16, the valveplate 16 bonded to the manifold 30 by ultrasonic welding, the cylinder12 having this valve plate 16 as its top (or distal end portion), thehousing (housing substrate material 44, cover 47, side members 45 and46) integrally including the cylinder 12, the valve 26 inserted into thecenter hole of the piston 14 and operating as the suction valve, thepiston 14 inserted into the cylinder 12, the coupling ring 34press-fitted into the spherical seat 37 as the recess of the lower part(or base bottom side) of the inside of the piston 14 and transmittingthe driving force of the reciprocating motion to the piston 14, theconnecting ring 36 integrally coupled with the coupling ring 34, thecrank shaft 38 inserted to the inner circumference of the connectingring 36, the driving shaft 40 pressure fitted into the crank shaft anddriven for rotation and the motor 42 for driving the driving shaft 40.As can be seen clearly from the drawing, the components are mainlyconnected and assembled in the vertical direction in the drawing andassembly itself is extremely simple and easy. Therefore, this pistonpump can be made compact in scale. Furthermore, mechanical fasteningmembers (screws, rivets, bolts and nuts, nails, etc, for example) thathave ordinarily been used for assembling these components are notnecessary. In other words, it can be the that assembly is made by usingnon-mechanical fastening members. Assembly by using non-mechanicalfastening members may mean bonding by bonding, deposition, welding, etcand assembly such as press-fitting, fitting, insert molding, insertion,etc (inclusive of detent of assembly component itself, latch mechanismby engagement member). The assembly step becomes short in time andproduction efficiency is high because assembly is made by suchnon-mechanical fastening members. In this embodiment, the manifold 30,the valve plate 16 and the cylinder 12 are bonded by ultrasonicdeposition, respectively. The valve 18 and the valve plate 16, the valve26 and the piston 14, the piston 14 and the coupling ring 34, theconnecting ring 36 and the crank shaft 38 and the crank shaft 38 and thedriving shaft 40 can be detachably assembled by fitting, respectively.

FIGS. 4 to 6 are views for explaining in detail the piston 14. The hole29 for fitting the valve is disposed at the center of the piston 14 insuch a manner as to communicate with the hollow portion 35 inside thepiston and a plurality of suction ports 28 is arranged around the hole.The umbrella portion of the valve 26 (see FIG. 3) of the valve 26 fittedinto the hole 29 covers these suction ports. The recess is formed below(or base bottom side) the hollow portion 35 inside the piston and thespherical seat 37 is disposed in the recess.

FIGS. 7 to 11 show the connecting ring 36 molded integrally with thecoupling ring 34 as the coupling member when the connecting ring 36 isviewed from various angles. A projection portion 34 a is formed aroundthe entire outer circumference of the coupling ring 34 and the curvatureof this projection portion 34 a is so set as to be capable of rotatingin, or engaging rotatably with, the spherical seat 37 (see FIG. 4)existing in the recess of the piston 14. The curvature of the projectionportion 34 a is a little smaller than the curvature of the sphericalseat 37, for example. In other words, the radius of curvature of thespherical seat 37 is a little greater than the radius of curvature ofthe projection portion 34 a. A hollow portion 34 b exists on the innercircumferential side of the coupling ring 34 and operates as an airpassage. The coupling ring 34 and the connecting ring 36 are coupled bya coupling portion 33 and are integrally molded.

When this integral member is viewed from the upper surface, therectangular coupling portion 33 can be seen through the hollow couplingring 34. Gaps 33 a are provided above and below the coupling portion 33and operate as passages for feeding necessary air to the suction ports28 of the piston 14. The connecting ring 36 has substantially flat outerand inner circumferential surfaces 36 a and 36 b. The crank shaft 38 isfitted into the ring opening portion 36 c as the space defined by thisinner circumferential surface 36 b.

FIGS. 12 to 15 schematically show the mode of engagement anddisengagement between the spherical seat 37 as the recess portion of thepiston 14 and the projection portion 34 a of the coupling ring 34. Thecoupling ring 34′ that exists inside the spherical seat 37 at asubstantially horizontal position when the piston is driven can rotatenot only in the circumferential direction of the piston 14 but also inthe direction corresponding to the movement in the axial direction asshown in FIG. 12. In the drawing, the member 14′ representingschematically the base bottom portion of the piston 14 is shown upsidedown in the reverse way to FIG. 1. The coupling ring 34 can be pivotallyrotated in this way when the connecting ring 36 protruding from thespherical seat 37 is moved back and forth and to the right and left.However, it is extremely difficult for the coupling ring 34 to fall offas such because the diameter of the opening 19 at the upper part of themember 14′ schematically representing the base bottom portion of thepiston 14 is sufficiently smaller than the diameter of the projectionportion 34 a of the coupling ring 34.

Therefore, to remove the coupling ring 34 from the recess portion havingthe spherical seat 37, the coupling ring 34 is tilted by an angle ofinclination a in such a manner that at least a part of the projectionportion 34 a protrudes from the opening 19 of the member 14′schematically representing the base bottom portion of the piston 14 onthe base bottom side (upper side in the drawing). Next, the connectingring 36 is pushed with the portion 19 a that is the edge of the opening19 and strikes the side surface of the connecting ring 36 as the supportpoint to allow a pulling force F for pulling out the coupling ring 34from the opening 19 to operate. At this time, the opening 19 is expandedby the outer circumferential surface of the projection portion 34 a in Pand Q directions. Because this expanding force operates on only theportion that keeps contact in practice, the original opening 19′ neednot be expanded as a whole but may be sufficiently expanded so as toform an elliptic opening 19. Therefore, the pulling force F need not bemuch great.

FIG. 16 is a view for explaining a gas leakage inspection step of thepiston pump according to this embodiment. The piston pump of theembodiment mainly handles a gas of a low pressure and is not consideredas a pressure container. Therefore, a predetermined inspection isnecessary. The greatest square in the drawing represents an inspectionapparatus 50. The inspection apparatus 50 has a round start switch 54 atan upper part of a front panel and a green lamp 56 and a red lamp 58indicating the inspection result are arranged below the start switch 54.The inspection apparatus 50 has therein a 100 cc-tank 60 (capacity isdifferent when inspection standard is different). The tank 60 isconnected to a pipe 62 extending outward. A sensor 52 is fitted to thetank 60 and measures the change of the pressure inside the tank. A powersource is disposed at a lower right position of the inspection apparatus50 and can be connected to the pump, etc, as the inspected body. A pumppre-assembly 11 as the inspection object is connected to the distal endof the pipe 62. Another pipe 64 is connected in a T shape to anintermediate part of the pipe 62. A valve 66 is arranged at anintermediate part of the pipe 64 and is connected to an external pump68. Here, the power source is used when the inspection object can byitself make pressurization and is not particularly necessary in thisembodiment because the external pump 68 conducts pressurization.

FIG. 17 shows the pump pre-assembly 11 as the inspection object shown inFIG. 16. The inspection object mentioned hereby includes the valve plate16 and the exhaust valve 18 deposited to the top of the cylinder 12 andthe manifold 30 deposited to the valve plate 16 in the piston pump ofthe embodiment described above exclusive of the piston and itsaccessorial components and the motor and its accessorial components.Air-tightness of the space 31 defined by the valve plate 16 and themanifold 30 or the air chamber is the inspection object in theinspection and the piston, etc, need not be inspected. To carry out theinspection, the valve 66 is first opened and the pressure inside thetank is set to approximately 300 mmHg by the external pump 68 (see FIG.16). At this time, the pump pre-assembly 11 as the inspection object maybe connected so that it is not affected by the pressurization step bydisposing still another valve at an intermediate part of the pipe 62.When a predetermined pressure is reached by the external pump 68, thevalve 66 is closed, the start switch 54 is turned ON and the inspectionis started. When the absence of leakage to a certain extent is confirmedafter the passage of approximately 15 seconds, the green lamp 56 is litand when the leakage is great, the red lamp 58 is lit. As describedabove, in the piston pump according to this embodiment, the inspectioncan be made under the state of the piston pump pre-assembly, anddefective products can be rejected at an early stage and productivitycan be improved.

FIG. 18 is a graph showing an ultimate pressure and consumed power whenthe piston pump of this embodiment is operated at a predeterminedcapacity (100 cc in the drawing). The result of a diaphragm pump havinga similar capacity is indicated by broken line. In this graph, a largeconsumed current means the necessity of large power and when comparisonis made at the same pressure, lower power efficiency means greaterconsumed power. In the piston pump according to this embodiment, thecurrent when a pressure of approximately 5 KPa is reached isapproximately 180 mA and the current value becomes greater as thepressure rises. The current value is approximately 270 mA at a pressureof approximately 27 KPa necessary for a blood pressure monitor that canbe conceived as an application example of this piston pump. In contrast,in the diaphragm pump, the current value is approximately 270 mA atapproximately 5 KPa and approximately 320 mA at approximately 27 KPa. Inother words, it can be understood that the piston pump according to theembodiment has the advantage that it is excellent in current efficiencyin a range that is used in practice.

FIG. 19 illustrates a production process of the piston pump according tothis embodiment. First, a valve that is to become the exhaust valve 18is fitted into the hole 24 of the valve plate 16 to fabricate a valveplate assembly (S-01). Next, the cylinder 12, the valve plate assemblyand the manifold 30 are bonded by ultrasonic deposition to fabricate thepiston pump pre-assembly (S-02). The leakage inspection described aboveis carried out for this piston pump pre-assembly as the inspectionobject (S-03). Those inspection objects which are approved in theinspection are sent to the next step and those rejected are repaired ordiscarded. The piston assembly is fabricated in parallel with the stepsdescribed above. First, the valve that is to become the suction valve 26is fitted into the hole 29 of the piston 14 to fabricate the pistonequipped with the valve (S-11). Next, the coupling ring 34 having theconnecting ring 36 coupled thereto is press-fitted (inserted) into thepiston with the valve to fabricate the piston assembly (S-12). The crankshaft 38 is press-fitted to the driving shaft 40 of the motor 42 inparallel with the production step described above and the motor equippedwith the shaft is produced (S-21). The crank shaft of the motor equippedwith the shaft is inserted into the connecting ring of the pistonassembly described above and a piston-cam-motor provisional assembly isproduced (S-13). The piston of the piston-cam-motor provisional assemblyis inserted into the cylinder of the piston pump pre-assembly describedabove and at the same time, the motor is fitted to the housing (S-04).The cover 47 of the housing is closed and the projection 43 is meshedwith the opening 51 to complete the piston pump of this embodiment(S-05). As described above, the piston pump according to this embodimentcan be produced with a drastically smaller number of production stepswhile the gas leakage test is inserted into the production steps.

FIG. 20 is a sectional view showing a piston pump 10′ according toanother embodiment. Since the basic construction is the same as the oneshown in FIG. 1, common portions are omitted. The cover 47 is closed andthe plenum 53 is defined by the right side portion 47 a of the cover 47,the side member 46, the partition plate 48 a, the shaft opening portion48 b, the partition plate 48 c on the cover side and the piston 14.Because the pressure of this plenum 53 is reduced by the operation ofthe pump chamber 22 of the piston pump 10′, air is sucked through theshaft opening portion 48 b. The noise generated at the sliding portionscan be prevented from going out when the components having a largenumber of sliding portions are encompassed in this way by the enclosure.

FIG. 21 is a sectional view showing a piston pump 10″ according to stillanother embodiment. Because the basic construction is the same as theone shown in FIG. 1, the common portions are omitted. This piston pump10″ is directed to suction or pressure reduction but not to exhaust.Therefore, handle portions of the valves 18 and 26 are inserted andfixed from the lower side in the drawing into the insertion holes 24 and29 in the valve plate 16 and the piston 14. In this construction, airmoves in the reverse direction to the explanation of FIG. 1, thepressure of the space 31 is reduced and air is sucked from outsidethrough the discharge port 32. A wall 73 at the depth that is omittedfrom FIG. 1 for simplification is expressed beyond the crank shaft 38.Holes 78 and 78 for accommodating projections 76 and 76 disposed on thecover 47 are disposed at both ends of the wall 73 at the depth. Thecover 47 can be kept under the closed state when these projections 76and 76 are fitted (inserted) into the holes 78 and 78, respectively.Fitting between the projection 76, 76 and the holes 78, 78 may be loosefit but is preferably close fit to a certain extent. Fitting may also besliding fit. This is to obtain desired pull-out resistance. The shapemay be a simple rod shape or a rod shape having a projection at anintermediate part. When a polymer material such as a plastic material isused, the shape is more preferably the simple rod shape. At this time,the partition plate 72 having the opening on the side of the housingsubstrate material 44 and the partition plate 74 on the side of thecover 47 butt against each other and form the plenum 53 shown in FIG.20.

FIGS. 22 and 23 illustrate a housing 70′ equipped with a cylinder thatis produced by providing a closing mechanism of the cover 47 shown inFIG. 21 to the housing 70 with the cylinder shown in FIG. 3. When theshape is such a planar shape, molding by injection molding, etc, becomeseasier and more preferable. Four projections 76 constituting the closingmechanism of the cover 47 protrude upward. Each side member 45 operatingas the hinge is under the return state (FIG. 23) from the state where itis largely bent (FIG. 22) and its form is shaped so that the closingmechanism can operate. It can be seen that the wall covering the sidesurface of the plenum 53 is molded integrally with the cylinder 12.Holes 78 are bored at four corners of this rectangular wall and can fitto the projections 76.

FIG. 24 illustrates the state where the motor 42 is accommodated halfinside the motor housing. The driving shaft 40 of the motor 42 ispressed into the crank shaft 38 and the crank shaft 38 is inserted intothe ring opening portion 36 c as the inside space of the connecting ring36. The coupling ring 34 coupling with the connecting ring 36 engageswith the spherical seat 37 of the piston 14 (see FIG. 2). When the cover47 is pushed in from this state, the pump assembly can be easilyfabricated. The valve plate is hereby omitted for simplification butsuch an assembly can be assembled after the valve plate is bonded byultrasonic deposition in practice.

FIG. 25 illustrates the motor 42 used in this embodiment. Terminals 42 aand 42 b protruding up and down from an insulating end face are providedon the opposite side of the driving shaft 40 of the motor 42 and supplynecessary power to the motor 42. Connection is easy because theseterminals 42 a and 42 b are exposed from the opening portion of the sidemember 45.

FIG. 26 is a sketch showing the piston pump 10′″ under the state inwhich the cover 47 shown in FIG. 24 is fitted. The valve plate 16 isdeposited to the top of the cylinder 12 and the manifold 30 having thedischarge port 32 is further deposited. The direction of the dischargeport 32 faces right in the drawing like a beak of a duck moving forth ona water surface contrary to the case of FIG. 1.

Referring to FIGS. 27 to 30, a control main portion 80 of the bloodpressure monitor having the pump assembled therein will be explained. Abattery accommodation portion 92 is arranged to the left in an elongatedform inside the rectangular control main portion 80. A control portion90 of a printed wiring board (PCB) is arranged on the right side of thisbattery accommodation portion 92. A power source portion 90 a isarranged in this control portion and supplies power to the pump. A pumpaccommodation portion 82 is defined by a transverse pump support rib 84a and a longitudinal pump support rib 84 b on the further right of thecontrol portion 90. A solenoid valve 86 is arranged above the controlportion 90 and is opened and closed in accordance with the control ofthe control portion 90. An opening portion 88 at the center of thesolenoid valve 86 is an air discharge port and air is sent from thenceto a cuff pressing an arm or a wrist. FIG. 28 illustrates the section ofa substrate 81 for putting the components described above on a substratesurface 81 a. Both ends are obliquely lifted up to a certain extent sothat a display surface 81 b of the blood pressure monitor at the lowerpart in the drawing can be neatly designed.

FIG. 29 illustrates the state in which a diaphragm pump 910 is stored inthe pump accommodation portion 82 shown in FIG. 27. The pump supportribs 84 a and 84 b effectively support the diaphragm pump 910 and poweris supplied from the power source portion 90 a to the electrodeterminals 910 a and 910 b through lead wires. A discharge port of thediaphragm pump 910 is connected by a flexible tube 83 in such a manneras to send discharge air to a suction port 87 of the solenoid valve 86connected to the other end of the flexible tube 83. FIG. 30 illustratesthe case where the diaphragm pump 910 is replaced by the piston pump10′″ of the embodiment shown in FIG. 26. Air is sent from the dischargeport 32 of the piston pump 10′″ to the suction port 87 of the solenoidvalve 86 through the tube 83 connected in the same way as in FIG. 29.The rest of the constructions and operations are the same and aretherefore omitted. It can be understood from these drawings that thepump has high versatility because the piston pump 10′″ of FIG. 26 can beeasily fitted to the control main portion 80 of the blood pressuremonitor using the diaphragm pump.

FIG. 31 shows in section a piston pump 10″″ according to still anotherembodiment. The explanation of overlapping portions will be omittedbecause the construction is basically the same as the constructionsshown in FIGS. 1, 20 and 21. Each wall as the enclosure encompassing theplenum 53 is constituted by a partition plate 72′ having a smaller shaftopening portion, a partition plate 74′ of the cover 47, the side member46 and a right side portion 47 a of the cover 47. A rip-seal type rubberseal 77 is fitted to the partition plates 72′ and 74′ to increaseair-tightness. The rubber seal 77 need not be disposed whenair-tightness is not much required. The side member 46 has a suctionport 79 facing right. According to this construction, a pump capable ofsucking and exhausting (from the discharge port 32), though small insize, can be provided. Incidentally, the discharge port 32 can bedirected in all directions as described so far and this can beaccomplished by an extremely convenient method of changing the directionat the time of deposition of the manifold 30.

The piston pump of the present invention described above includes thesuction port through which the gas sucked in accordance with the changeof the volume of the pump chamber defined by the cylinder and the pistondue to the reciprocating motion of the piston inserted into the cylinderpasses, the exhaust port through which the gas exhausted in accordancewith the change of the volume of the pump chamber passes, the suctionvalve disposed at the suction port arranged at the top of the piston,and the exhaust valve disposed at the exhaust port arranged at the topof the cylinder. Therefore, the piston pump has the advantages that theconstruction is simple, the number of components is small and the scalecan be rendered compact. Consumed current is small and pump efficiencyis high.

1. A piston pump comprising: a cylindrical cylinder; a pistonreciprocating inside the cylinder; a suction port through which gassucked into a pump chamber defined by the cylinder and the pistonpasses; and an exhaust port through which the gas discharged from thepump chamber passes; wherein the piston pump sucks the gas through thesuction port and discharges the gas through the exhaust port as thevolume of the pump chamber is changed by reciprocating motion of thepiston; wherein the suction port is arranged at a top of the piston witha suction valve, which opens as the volume of the pump chamber isincreased; and wherein the exhaust port is arranged at a top of thecylinder with an exhaust valve, which opens when the volume of the pumpchamber is decreases.
 2. The piston pump according to claim 1, whereinthe suction valve is arranged on a side of the pump chamber.
 3. Thepiston pump according to claim 1, wherein the exhaust valve is arrangedon an opposite side to the pump chamber of the top of the cylinder. 4.The piston pump according to claim 1, wherein the piston has an openingcommunicating with the suction port on an opposite side to the pumpchamber, wherein the opening is arranged so as to allow air suckedthrough the suction port into the pump chamber to pass and a plenumcapable of storing the air to communicate with the opening; and whereinthe plenum is encompassed by an enclosure having at least one plenumsuction port.
 5. A piston pump including a cylindrical cylinder having atop portion; a piston reciprocating inside the cylinder; a suction portthrough which gas sucked into a pump chamber defined on a side of thetop portion of the cylinder by the cylinder and the piston passes; andan exhaust port through which the gas discharged from the pump chamberpasses; wherein the piston pump sucks the gas from the suction port anddischarges the gas through the exhaust port as a volume of the pumpchamber is changed by reciprocating motion of the piston; wherein thesuction port is arranged at the top portion of the cylinder with asuction valve, which opens when the volume of the pump chamber isincreased; and the exhaust port is arranged at the piston with anexhaust valve, which opens when the volume of the pump chamber isdecreased.
 6. The piston pump according to claim 5, wherein the suctionvalve is arranged on a side of the pump chamber.
 7. The piston pumpaccording to claim 1, wherein the piston engages with a coupling memberin such a manner that the coupling member is capable of turning in acircumferential direction thereof, and wherein the coupling member isconnected to a connecting member driven such that the engaged piston isreciprocated inside the cylinder.
 8. The piston pump according to claim7, wherein the piston comprises therein a recess portion formedcontinuously in the circumferential direction of the piston and engagedwith the coupling member, the recess portion including at least a partof a first predetermined spherical surface; wherein the coupling memberhas a projection portion formed continuously in the circumferentialdirection such that the projection portion corresponds to the recessportion, the projection portion including at least a part of apredetermined second spherical surface to engage with the recess suchthat the projection portion is capable of turning in the circumferentialdirection and in an axial direction; and wherein the piston reciprocateswhen the projection portion and the recess portion engage with eachother so as to transmit driving force from the connecting member to thepiston.
 9. The piston pump according to claim 1, wherein at least aportion of the piston sliding on an inner wall of the cylinder iscomposed of a self-lubricating material.
 10. The piston pump accordingto claim 1, wherein the cylinder comprises a top plenum defined by a topenclosure fixed to the top portion of the cylinder and a motor housingfixed at a position spaced apart by a predetermined distance from thetop portion such that the cylinder is connected and fixed to at least apart of the motor housing; wherein the motor housing is composed of abase portion fixed to the cylinder such that the base portion holds amotor for driving the piston so as to reciprocate inside the cylinderand a cover portion disposed along the base portion such that the coverportion fastens the motor by sandwiching the motor with the baseportion; and wherein the cover portion and the base portion are engagedwith a connecting mechanism capable of engagement and disengagement. 11.The piston pump according to claim 1, wherein the piston pump isconnected to a blood pressure monitor.
 12. A piston pump in which apiston reciprocates inside a cylinder having a cylinder head forpressurization, the piston pump is characterized in that: (1) an innerdiameter of the cylinder is not exceeding approximately 20 mm; (2) athroughput of the piston pump is not exceeding approximately 6.0liters/min; (3) pressurization characteristics thereof can be maintainedeven after approximately 10,000 reciprocating motions of the piston; and(4) the cylinder and the cylinder head are non-mechanically coupled. 13.A method of producing a piston pump including a cylindrical cylinder, apiston reciprocating inside the cylinder; a suction port through whichgas sucked into a pump chamber defined by the cylinder and the pistonpasses and an exhaust port through which the gas discharged from thepump chamber passes; the method comprising the steps of: producing apiston pump pre-assembly comprising the cylinder and a cylinder topportion in which the exhaust port is formed; conducting a leakageinspection of the piston pump pre-assembly; and producing a piston pumpby further assembling components to the piston pump pre-assembly.
 14. Ablood pressure monitor utilizing the piston pump according to claim 1.